Environmental stress and a decline in cellular defense during aging are major factors in etiopathogenesis of many age-linked disorders including cataract. Since local antioxidant capacity determines the susceptibility of a cellular target to oxidative stress, it will be crucial to determine the impact of regulation of a protectiv molecule like Peroxiredoxin6 (Prdx6) on oxidative stress and vice versa. Using targeted inactivation of Prdx6 gene, we have shown that aging lens epithelial cells (LECs) and Prdx6-deficient LECs or eye lenses are vulnerable to cell death or cataractogenesis, suggesting that Prdx6 plays a pivotal role in lens defense. However, mechanisms underlying the reduced activity of Prdx6 are not known. Recently, very intriguing links have been found among oxidative stress levels and a posttranslational modification, Sumoylation of protein(s) and thereby the modulation of protein expression, activity and stability. Ocular lens is constantly exposed to environmental stress. ROS are constantly produced intracellularly, if not removed, leads to deregulation of cellular redox status. Initial studies revealed that Prdx6 expression and activity are deregulated by Sumoylation, leading to loss of Prdx6's protective activity. The rationale for the present proposal is derived from our initial studies showing that (a) Prdx6 is a target for Sumo (Small Ubiqitin-like Modifier)1, and Sumoylation of Prdx6 reduces its activity and cell injury, as evidenced by Prdx6-deficent cells overexpressing Sumo1 and Prdx6 facing oxidative stress; (b) Sumo1-specific protease (Senp)1 is inactivated and Sumo1 is increased in LECs facing oxidative stress and aging LECs; (c) Sumoylation of Sp1, activator of Prdx6, attenuates its activation potential; (d) Delivery of protein transduction domain (TAT)-linked Prdx6K122R/K142R mutant at Sumo1 sites to LECs/lenses provides enhanced cytoprotection against oxidative stress. We hypothesize that aberrant Sumoylation process deregulates Prdx6 function(s) during oxidative stress/aging, and that with aberrant Sumoylation of Prdx6 and its transactivator Sp1, Prdx6 functions go awry, leading to cell malfunction and, in turn, may lead to cataract formation. The overall goal of this proposal is to delineate Sumoylation-mediated-aberrant signaling that causes reduced expression and activity of Prdx6, as well as to uncover the pathogenic processes initiated by loss of Prdx6 activity through three specific aims: (1) Document and examine the effect of oxidative stress and aging on Prdx6 Sumoylation and on Prdx6 protein integrity and protective activity; (2) Determine the effect of Sumoylation/deSumoylation of Sp1 on Prdx6 gene transcription in cells facing oxidative stress or aging cell and Prdx6-/--deficient LECs as a model for aging; (3) Evaluate the potential of TAT-linked Prdx6 mutated at Sumo1 sites in protecting cells/lenses facing oxidative stress in vitro. The Shumiya cataract rat will be used to test TAT-linked Prdx6 in preventing/delaying the progression of cataract formation. The studies should allow us to design new therapies to attenuate the deleterious signaling that causes insults in the elderly and in situations involving physiological and environmental stress, and ultimately to prevent diseases associated with oxidative stress or aging, in general.